Re: (IAAC) Obj: M33 + Help me with M81!
[To 'meteorobs' readers: Forgive this somewhat off-topic crosspost. -Lew]
Natko Bajic wrote:
>I've also heard on IAAC that several people have seen M81 with naked eye.
>I would appreciate any information about doing it because I'm planning a
>trip to a 6500ft mountain this winter, where I expect limiting magnitude
>of 7, or maybe even more. Thanks!
Sorry for the late reply, Natko - Leonids have been keeping me rather busy
in my other life as a meteor observer!
I have seen M81 several times now naked eye... The most recent was from a
professional observatory in China during this year's Leonids: name of the
site was Xinglong Station - about 120km "as the crow flies" from Beijing.
And "as the photon travels" also! The light dome from Beijing was quite a
distinct nuisance when facing directly WSW.
However, at the zenith and down to a surprisingly low elevation facing in
most other directions, I was surprised to note how dark the sky was: far
better than I'd expected, and even better than I had hoped for this site.
My naked-eye "Limiting Magnitudes" (IMO method) for the four nights I was
recording meteors, ranged from 7.2 to 7.5. (For comparison, in my favorite
haunt on Long Key, FL, USA, I have regularly achieved 7.5 in the past. And
from both the mountains of SW New Mexico, and from the 9000' site on Mauna
Kea in Hawai'i, I have most likely logged down below 7.8 or so. The last is
uncertain, as IMO's conversion tables stop at 7.5. Please note that as with
any measurement of sky darkness, *your own mileage WILL of course vary*!)
To see faint objects, the key is simply knowing their EXACT location, and
being *really* dedicated to dark adaptation: recall that the eye can take
as long 30 minutes OR MORE to become fully adapted. And if there is any
white light at all (even a distant flashlight), or if your "red light" is
in fact bright enough to do ANYTHING but look at a watch WHILE SQUINTING,
then you will simply never reach full adaptation. (This latter is the most
common reason why people decide their "eyes aren't that good": in fact,
their eyes may be fine, but their observing technique could be improved.)
Another critical factor is rest, energy and comfort: If you are fatigued,
craning your neck, hungry, cold, or have any other "physical distraction",
you are *guaranteed* not to perceive faint light to your full potential.
The same is true for even slight elevation oxygen deprivation, at least
in my case. Also I believe, excited or "chatty" conversations and other
"psychological" distractions can have an effect on faint perception too.
In any case from Xinglong Station, at its highest point before dawn, M81
was a quite distinct object to careful averted vision. And early in the
night, M33's inner part had been readily visible to direct vision. After
4 days, my "naked-eye Messier count" (for the times I wasn't distracted
by a meteor storm that is!) was 27... It might have been higher, had I
managed to get enough sleep during the day to start sky watching before
the Leonid radiant rise those nights! As it was, I never started observ-
ing any night before 22:30 local time, and missed some Summer Messiers.
BTW, aside from Beijing's light dome (and occasional flashes of white
light from *professional astronomers* working in nearby domes!), this
Xinglong Station was a definite "Bortle Class 2" site during my visit.
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